I have a Knock Out rose that has a disease called witch’s broom I think. I have done some research on this disease and it says that there is nothing to do but destroy the rose, but this research was about five years old. Has there been any additional information on this? This is such a beautiful bush and I hate to dig it up. We also tried spraying it, but it didn’t seem to do any good. Can you help me please?
The Gardener’s Answer
Hello, Bettie: Knock Out roses for the most part are quite disease-resistant. In horticulture, witch’s broom is a term used to describe a specific type of growth habit. Described as small clumps of short twigs, these witch’s brooms develop when a bud is injured, and as a result the plant produces many weak shoots as opposed to one healthy shoot as a survival technique. In some cases witch’s broom is a secondary response to the real problem. Spraying will not be effective if we are not sure what we are spraying for. Witch’s broom is not common with roses and I would not suspect that this is what is going on with your rose. Of course without seeing it I cannot say for certain. Finding out the real reason why your rose is unhappy is essential to nurturing it back to health. It is difficult to say what the problem is without having any details. If you could give me more specific information about what is going on with your rose I can be of more help. You are welcome to send a picture to firstname.lastname@example.org or you can always take a sample of your rose to your county Extension office. The Green County offices are located at 106 South Public Square. You can reach them at (270) 932-5311 or visit their Web site at http://ces.ca.uky.edu/green. The horticulture/agriculture agents will be able to help you and they can send it off to the University of Kentucky for diagnosis if necessary.